Automated systems for measuring the concentration of analytes in a sample have been developed using a number of analytical techniques such as chromatography or mass spectrometry. For example, co-assigned U.S. patent application Ser. No. 10/094,394, entitled “A Method and Apparatus for Automated Analysis and Characterization of Chemical Constituents of Process Solutions,” filed Mar. 8, 2002, the contents of which are hereby incorporated by reference in their entirety, discloses an automated in-process mass spectrometry (IPMS) apparatus for identifying and quantifying chemical constituents and their reaction products in process solutions.
One type of process solution which the IPMS apparatus in the above-mentioned application may analyze is a copper electroplating bath for the deposition of copper structures on semiconductor wafers. The bath comprises a relatively concentrated acidic aqueous copper sulfate solution. Plating topology is controlled by organic plating solution additives within the copper sulfate solution that function to either suppress or accelerate the plating process. These additives experience electrochemical breakdown during the plating process and can be lost by drag out or by becoming trapped within the film. However, the achievement of void-free plating in the vias and trenches of sub-micron high-aspect-ratio structures requires very tight control of additive levels. Unlike indirect measurement methods such as cyclic voltametric stripping (CVS) that monitor the effectiveness of the plating solution, the IPMS apparatus discussed above allows a user to directly measure the additive concentration plus the breakdown products in the electroplating bath to ensure a defect-free deposition process.
High sensitivity quantification of the organic additives and their breakdown by-products in the electroplating bath is hampered by the relatively high concentration of sulfuric acid and copper sulfate matrix within the bath. These relatively high concentrations of sulfuric acid, plus sulfate and copper ions obscure the detection and quantification of the organic additive ions because ionization of the higher concentration ions is statistically more likely in the ionization source of the mass spectrometer. Thus, the copper sulfate should be removed from the sample and/or the pH adjusted to quantify the organic additive concentration. Similarly, other metrology techniques such as flow injection analysis and chromatography often require the removal of chemical constituents that may hamper the quantification of an analyte of interest.
Accordingly, there is a need in the art for automated systems for the removal of chemical interferents prior to a chemical analysis.